Balanced support for overhung table of machine tools, particularly for milling machines



CHIAIA P. 3,295,418 BALANCED SUPPORT FOR OVERHUNG TABLE OF MACHINETOOLS, PARTICULARLY FOR MILLING MACHINES Jan. 3, 1967 v 2 Sheets-Sheet lFiled Dec.

INVENTOR ATTORNEY 3,295,418 ABLE OF MACHINE FOR 5 2 Sheets-Sheet 2 FiledDec. 29; 1964 m mk INVENTOR ATTORNEY United States Patent 3,295,418BALANCED SUPPORT FOR OVERHUNG TABLE OF MACHINE TOOLS, PARTICULARLY FORMILL- ING MACHINES Paolo Chiaia, Via Ghiberti 11, Milan, Italy FiledDec. 29, 1964, Ser. No. 421,906 9 Claims. (Cl. 9058) This inventionrelates to a balanced support for overhung tables of machine tools, andparticularly-though not exclusivelyfor milling machines.

As already well known, machine tools are often fitted with overhungtablesusually work tableswhich can be adjusted in three directionsperpendicular with respect to each other, one of such directions beingvertical.

The vertical adjustment is usually that which requires a movement of thegreatest mass, since the table assembly must be rather heavy to preventany undesirable vibration from being transmitted to a workpiece. Thus,in the conventional designs of machine tools, an overhung table isprovided which is guided in dovetail guides, and is lifted or lowered byan elevating spindle.

It is also well known that the stability and rigidity of an overhungtable or knee in milling machines is rather uncertain, due to the factthat the whole weight of such knee assembly is usually to be supportedby the elevating spindle, which is therefore subjected to an unduly highwear, and at any rate, the vertical adjustment of such knee alwaysrequires an appreciable physical effort.

To prevent the above drawbacks, the invention provides a device by whichthe weight of an overhung table or knee is automatically balanced.

To the above purpose, a support for overhung tables of machine tools isprovided, which is characterized in that the overhung table or knee,slidingly fitted in dovetail guides, is supported by a movable arm,against the action of spring means.

One end of such arm is advantageously pivotally connected with aslipper, which is slidingly fitted in guides provided on the lower faceof the knee, while the opposite end of same arm is pivotally connectedwith the stationary frame of the machine, and having a toothed sector,fast with latter end, in mesh with a rack, which is moved against theaction of said spring means.

The invention will be better appreciated from a consideration of thefollowing description, taken with the accompanying drawing, being bothdescription and drawing given as a not restrictive example only.

In same drawing:

FIG. 1 is a diagrammatic side view of a machine tool equipped with thesupport according to the invention,

FIG. 2 is a partial section taken on the line 11-11 of FIG. 1, and

FIG. 3 shows a detail of the section taken on the line IIIIII of FIG. 2.

Referring to above figures, a machine tool 1 is equipped with anoverhung table or knee 2, that is slidingly fitted on guides 3.Additional guides 4, designed to accommodate a slipper 5, are providedon one side (preferably the lower side) of said knee (see also FIG. 2).The forkshaped end 7 of a lever 8 is pivotally connected with saidslider 5, while the opposite end of said lever is pivotally connected,as in 9, with the machine bed 10. A toothed sector 11, fast with 9, ordirectly with the related end of lever 8, is in mesh with a rack 12,that is slidingly fitted, against the action of a spring 14, on a rod13, located within the machine bed.

Obviously, more than one toothed sector 11-and as many guides 13 andsprings 14may be provided. In fact, in a preferred embodiment form, twoof such sectors, symmetrically located with respect to lever 8, areprovided. One end of spring 14 is set against the rack 12,

, 3,295,418 Patented Jan. 3, 1967 ice I while the opposite end of'samespring is set against an inside threaded bush 15, which is screwed ontothe threaded end 16 of guide 13. One end 17 of said bush 15 projects outof machine base, thus allowing same bush to be screwed into, or out ofguide 16 by means of a suitable spanner, thereby to adjust thepro-stressing of springs 14.

As it can be readily appreciated, the operation of the device isunusually simple. The weight of knee 2 is balanced, through the lever 8and the gearing 11, 12, by the springs 14, and it is to be noted thatthe force exerted by the weight of knee 2 on the arm 8 changes as theknee is lifted or lowered; more precisely, an increase in such forceoccurs when the knee is lowered, and conversely a decrease is noticedwhen the knee is lifted, proportionally to reaction exerted by thespring 14, which is greater when the knee is lowered, and smaller whenthe knee'is lifted,

There follows an automatic balancing of the system of forces acting onthe lever 8, and as a final result, a balancing of knee 2.

Moreover, as it can be noticed, the spacing between the two guides 4 isprogressively narrowed. A taper gib 18 is fitted between the slider 5and one of said guides, and more precisely the guide showing the surface4a which is inclined with respect to the longitudinal axis XX ofoverhung table 3. Said gib is kept firmly pressed against said surface4a by the two screws 30, that are passed through elongated holes 31 asformed in same gib. Thus, the gib can be axially adjusted by means ofthe grip 19 which is fitted in a plate 32, fast with the knee 2 in suchmanner that it can be turned, but not axially shifted. The end of samegrip 19 is threaded, and can be screwed into a suitably threaded hole ofgib. Due to the taper of the gib, when it is moved in one direction, theslider 5 is locked.

It goes without saying that the knee may be lifted or lowered by anyconventional system, e.g. by means of a worm, preferably fitted betweenthe two guides 3, and that can be driven either manually or, since theweight of the knee is balanced, even by means of a fractional motor.

While the invention has been described in detail with respect to certainnow preferred embodiment forms thereof, it will be understood by thoseskilled in the art, after understanding the invention, that variouschanges and modifications may be made, without departing from the spiritand scope of same invention, and is intended, therefore, to cover allsuch changes and modifications in the appended claims.

What I claim is:

1. In a machine tool of the type having a vertically movable carriage,in combination, support means; a cantilevered carriage having a firstportion supported by said support means for substantially verticalmovement therealong and having a second portion spaced from said supportmeans; and biasing means operatively connected to said second portion ofsaid carriage for exerting thereon an upwardly directed force inopposition to the force of gravity, said upwardly directed forceremaining substantially constant during vertical displacement of saidcarriage so that such vertical displacement may be accomplished withrelatively little effort.

2. In a machine tool according to claim 1, said biasing means comprisinga slide member movable along said carriage in directions toward and awayfrom said support means, resilient means carried by said support meansand cooperating with said slide member for exerting said upwardlydirected force on said carriage via said slide member, and means forincreasing the bias of said resilient means in response to movement ofsaid slide member along said carriage in a direction from said firstportion toward said second portion of the latter.

3. In a machine tool according to claim 2, said biasing means furthercomprising motion transmitting means articulately connecting saidresilient means with said slide member, said slide member being adaptedto move horizontally with respect to said carriage in response tovertical displacement of the latter and to transmit to said carriage thebiasing force exerted by said resilient means.

4. In -a machine tool according to claim 3, said motion transmittingmeans including pivot means fixed to said support means and a leverturnably mounted on said pivot means, said lever having an end spacedfrom said pivot means and articulately connected to said slide member sothat said lever turns about said pivot means in response to horizontalmovement of said slide member along said carriage when the latter isvertically displaced.

5. In a machine tool according to claim 4, wherein said pivot means islocated closer to said first portion of said carriage than to saidsecond portion.

6. In a machine tool according to claim 5 wherein the end portion ofsaid lever in the region of said pivot means is formed as a toothedportion, said biasing means further comprising an elongated rod fixed tosaid support means, a rack member slidable along said rod and meshingwith said toothed portion of said lever, and said resilient meanscomprising a coil spring surrounding said rod and biasing said rackmember in a direction to produce said upwardly directed force on saidcarriage.

7. In a machine tool according to claim 6, said spring being acompression spring and said rack moving in a direction to compress saidspring when said carriage is displaced downwardly.

8. In a machine tool according to claim 2 said combination furthercomprising adjusting means operatively connected to said resilient meansfor adjusting the bias thereof.

9. In a machine tool according to claim 2 further comprising lock meansoperatively connected to said slide WILLIAM W. DYER, JR., PrimaryExaminer.

G. A. DOST, Assistant Examiner.

1. IN A MACHINE TOOL OF THE TYPE HAVING A VERTICALLY MOVABLE CARRIAGE,IN COMBINATION, SUPPORT MEANS; A CANTILEVERED CARRIAGE HAVING A FIRSTPORTION SUPPORTED BY SAID SUPPORT MEANS FOR SUBSTANTIALLY VERTICALMOVEMENT THEREALONG AND HAVING A SECOND PORTION SPACED FROM SAID SUPPORTMEANS; AND BIASING MEANS OPERATIVELY CONNECTED TO SAID SECOND PORTION OFSAID CARRIAGE FOR EXERTING THEREON AN UPWARDLY DIRECTED FORCE INOPPOSITION TO THE FORCE OF GRAVITY, SAID UPWARDLY DIRECTED FORCEREMAINING SUBSTANTIALLY CONSTANT DURING VERTICAL DISPLACEMENT OF SAIDCARRIAGE SO THAT SUCH VERTICAL DISPLACEMENT MAY BE ACCOMPLISHED WITHRELATIVELY LITTLE EFFORT.